The present invention relates to an electronic bridge module, specifically to a high power metal oxide semiconductor half bridge module for an internal combustion engine starter/alternator circuit in which the module has a very low inductance.
Starting an internal combustion engine and rectifying the voltage generated by an alternator once the engine is running places high demands on the electronic circuitry required to support these functions. A typical starter/alternator requires minimum voltage drop at its input and an immediate torque current to mechanically "crank" the engine. In order to minimize voltage drop and supply immediate current, the start/alternator circuit path must have a low resistance and an extremely fast current slew rate (di/dt). The circuit must perform these functions under extreme temperature conditions such as might be found in a typical automotive environment. For example, the circuit must be capable of supplying a 650 amp current at -25.degree. C. in a 42 volt system such that the current slew rate is faster than 1500 amps per microsecond.
An essential component of the starter/alternator circuit is a half bridge rectifier. The half bridge rectifier must be capable of supporting the characteristics described above. A typical half bridge rectifier is produced as a module employing metal oxide field effect transistor (MOSFET) devices. In order to achieve the desired performance characteristics and avoid device overvoltage and avalanche conditions, the low voltage silicon used in the MOSFET devices must provide a resistance path of less than 2 milliohms at 25.degree. C., and a maximum module inductance of 12 nH. Of course, the module must be of a size small enough to be mounted at a spot convenient to its placement within the starter/alternator circuit, typically as part of a bus bar assembly located in a motor vehicle's engine compartment.